1. Field of the Invention
The present invention relates to a display device and a method of fabricating a display device, and particularly, to a liquid crystal display device and a method of fabricating a liquid crystal display device.
2. Description of the Related Art
In general, flat panel displays, such as liquid crystal display (LCD) devices, commonly include an active device, such as a thin film transistor, provided at pixel regions to drive the display device. In addition, a driving method for the LCD device is commonly referred to as an active matrix driving type method, wherein the active device is disposed at respective pixel regions that are arranged in a matrix configuration to drive corresponding pixels.
FIG. 1 is a plan view of an LCD device according to the related art. In FIG. 1, a TFT LCD uses a thin film transistor (TFT) 10 as an active device. In addition, an N×M matrix configuration of pixels are arranged along longitudinal and transverse directions, and includes the TFT 10 formed at a crossing region of a gate line 3, which receives a scan signal supplied from a driving circuit of an exterior portion of the LCD device, and a data line 5, which receives an image signal. The TFT comprises a gate electrode 11 connected to the gate line 3, a semiconductor layer 12 formed on the gate electrode 11, which is activated when the scan signal is supplied to the gate electrode 11, and a source electrode 13 and a drain electrode 14 formed on the semiconductor layer 12. A pixel electrode 16, which is connected to the source and drain electrodes 13 and 14 to operate a liquid crystal material (not shown) by supplying the image signal through the source and drain electrodes 13 and 14 as the semiconductor layer 12 is activated, is formed on a display area of the pixel.
FIG. 2 is a cross sectional view along I-I′ of FIG. 1 according to the related art. In FIG. 2, the TFT 10 is formed on a first substrate 20 made of a transparent material, such as glass, and includes the gate electrode 11 formed on the first substrate 20, a gate insulating layer 22 deposited on an entire surface of the first substrate 20 upon which the gate electrode is formed 11, a semiconductor layer 12 formed on the gate insulating layer 22, source and drain electrodes 13 and 14 formed on the semiconductor layer 12, and a passivation layer 24 deposited on an entire surface of the first substrate 20. A pixel electrode 16, which is connected to the drain electrode 14 of the TFT 10 through a contact hole 26 formed on the passivation layer 24, is formed on the passivation layer 24.
In addition, a black matrix 32, which is formed on a non-display area (i.e., a TFT 10 forming area) and an area between pixels to prevent light from transmitting to the non-display area, and a color filter layer 34 for producing R(Red), G(Green), and B(Blue) colors are formed on a second substrate 30 made of transparent material, such as glass. The first and second substrates 20 and 30 are bonded together, and a liquid crystal material layer 40 is formed therebetween.
FIGS. 3A to 3I are cross sectional views of a fabrication method of an LCD device according to the related art. In FIG. 3A, a metal layer 11a is formed by depositing metal material on the first substrate 20, and a photoresist layer 60a is formed on the metal layer 11a and baked at a certain temperature. Then, light is radiated onto the photoresist layer 60a through a mask 70.
In FIG. 3B, a developer is applied to the photoresist layer 60a, and a photoresist pattern 60 is formed on the metal layer 11a. For example, when the photoresist is a negative photoresist, portions of the photoresist layer 60a that are not exposed to the light are removed by the developer.
In FIG. 3C, an etching solution is applied to the metal layer 11a. Accordingly, a portion of the metal layer 11a blocked by the photoresist pattern 60 remains, whereby a gate electrode 11 is formed on the first substrate 20.
In FIG. 3D, a gate insulating layer 22 is formed on an entire surface of the first substrate 20, and a semiconductor layer 12a is formed on the gate insulating layer 22. Then, a photoresist layer is deposited onto the semiconductor layer 12a, and a mask (not shown) is provided such that light is radiated onto the photoresist layer and developed to form a photoresist pattern 62 on the semiconductor layer 12a. Next, an etching solution is applied to the semiconductor layer 12a such that only a portion of the semiconductor layer 12a under the photoresist pattern 62 remains on the gate insulating layer 22.
In FIG. 3E, the photoresist pattern 62 (in FIG. 3D) is removed. Accordingly, a semiconductor layer 12 is formed on the gate electrode 11.
In FIG. 3F, a metal material is deposited on an entire surface of the first substrate 20, and a photoresist pattern (not shown) is formed using a mask (not shown). Then, the metal material is etched using the photoresist pattern (not shown) for forming a source electrode 13 and a drain electrode 14 on the semiconductor layer 12.
In addition, a passivation layer 24 is deposited on the first substrate 20 upon which the source and drain electrodes 13 and 14 are formed to protect the TFT. Then, a portion of the passivation layer 24 overlying the drain electrode 14 is etched using a photolithographic process to form a contact hole 26 in the passivation layer 24.
In FIG. 3H, a transparent material, such as indium tin oxide (ITO), is deposited onto the passivation layer 24, and patterned using a photolithographic process to form the pixel electrode 16 on the passivation layer 24. Accordingly, the pixel electrode 16 is electrically connected to the drain electrode 14 through the contact hole 26 formed in the passivation layer 24.
In FIG. 3I, a black matrix 32 and a color filter layer 34 are formed on a second substrate 30, the first and second substrates 20 and 30 are bonded together, and a liquid crystal material layer 40 is formed between the bonded first and second substrates 20 and 30.
In the fabrication method of FIGS. 3A to 3I, the source, drain, and pixel electrodes 13, 14, and 16 and/or the semiconductor layer 12 is formed using photolithographic processes that use a photoresist layer. However, use of the photoresist layer in the photolithographic process is problematic. First, the fabrication processes are relatively complex. For example, the photoresist pattern is formed through processes of photoresist coating, baking, exposure, and developing. In addition, in order to bake the photoresist layer, a soft-baking process is performed at a first low temperature and a hard-baking process is performed at a second higher temperature.
Second, a majority of fabrication costs lie with the fabrication of active switching devices. During fabrication of the active switching devices, a plurality of photoresist patterns are required. For example, the cost of forming the photoresist patterns is about 40-45% of the total cost of fabricating the LCD device.
Third, the process for forming the photoresist patterns produces massive amounts of environment pollutants that must be recovered during the fabrication process of the LCD device. In general, the photoresist layer is made by spin coating a photoresist material to achieve a certain thickness. Accordingly, large amounts of the spun-off photoresist material are not used and some amounts are unfortunately released into the environment. In addition, recovery of the spun-off photoresist material increases fabrication costs.
Fourth, since the photoresist layer is applied using the spin coating method, it is difficult to control the thickness of the photoresist layer. Accordingly, thickness of the photoresist layer is non-uniform. Thus, during removal of portions of the non-uniform photoresist layer, residual amounts of the photoresist layer are created that negatively impact operation of the active switching devices.